An allergy is a state of over-reactivity or hypersensitivity of the immune system of a pet to a particular substance called an ‘allergen’. Most allergens are proteins. The allergen protein may be of insect, plant or animal origin. Initial exposure of the dog, or more likely multiple exposures, to the allergen may over-sensitize the immune system, such that a subsequent exposure to the same or related allergen causes an over-reaction. This means that the immune response, which normally protects the dog against infection and disease, can be harmful. The actual immune reactions involved in allergies are quite complex. Most reactions involve an antibody in the blood called Immunoglobulin E (IgE). In an allergic reaction the allergen protein molecules combine with IgE antibody molecules and attach to a type of cell called mast cells, found in many tissues. When these cells are attached to the allergen, they break up and release potent chemicals such as histamines, which cause local inflammation. This inflammation causes the various signs associated with an allergic reaction.
What are the symptoms of allergies in dogs?
The most common symptom associated with allergies is itching of the skin, either localized (one area) or generalized (all over the body). Another group of symptoms involves the respiratory system with coughing, sneezing, and/or wheezing. Sometimes, there may be runny discharge from eyes or nose. The third manifestation involves the digestive system, and the dog may vomit or have diarrhea.
What are the common allergy-causing substances (allergens)?
A very large number of substances can act as allergens. Most are proteins of insect, plant or animal origin, but small chemical molecules known as haptens can also cause allergy. Examples of common allergens are pollens, mold spores, dust mites, shed skin cells, insect proteins such as flea saliva, and some medications.
What are the different types of allergies?
There are several ways of classifying allergies. Some examples of classifications include: the precipitating allergen (Flea Allergy); the route the allergen takes into the body (Inhalant Allergy, Skin Contact Allergy, Food Allergy); the immune reaction timing (Immediate Hypersensitivity, also called Anaphylaxis or Shock; and Delayed Hypersensitivity); the type of immune reaction (Types I to IV Hypersensitivity); or by outcome (Allergic Dermatitis or Allergic Eczema; Allergic Bronchitis). There are also inherited forms of allergy (Atopy).